Dogs not getting along

Question
QUESTION: Hi - I have an unusual situation: We have a F 6 yo Border Collie who's actually pretty low key (for a border!).  A few years ago we got an F lab/terrier mix rescue as a companion.  The terrier has often tried to dominate over the border and though we've tried to minimize it, the border didn't fight back, basically ignoring the terrier's bumping, etc.  The dogs got along well at other time, playing together, etc.

Last year, my daughter went off to college and took the terrier mix with her.  Two months ago we acquired a F rescue Border/lab mix who is very quiet and somewhat shy.  The two dogs got along fine.  But now, due to various circumstances, my daughter has brought the terrier mix back to stay with us.  Although eh household has been relatively quiet 90% of the time, the terrier has displayed suspicion regarding the newest dog, which is not surprising.  The problem is that several times, she has lunged at the lab/border, snapping at it and barking aggressively, particularly if she finds herself in close quarters.  The lab has not fought back other than barking and quickly moving away. When the attacks happen, I have scolded the terrier, the last time grabbing and rolling her onto her back to assert my authority.  What can I do to stop these fights and attempts at dominance?

ANSWER: What a lot of people do and that works well is to muzzle the terrier for while when she is around the other dogs esp the new one. That way nothing can happen but she can establish herself in the pack without hurting the other dog. since it's only the terrier and the other dogs aren't fighting with her,she is the only one that needs to be muzzled. a basket type muzzle is the best type to get for this situation

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QUESTION: So, it's alright letting the dog try to assert its dominance?  Obviously, there is a pecking order that has to work itself out, but I'm a little uncomfortable with the terrier pushing its way around the "pack."  Would taking her back through obedience training for a refresher be of any value?

Answer
As a trainer myself it doesn't hurt to put a dog through a refresher but it is always best to let dogs sort out there order,or they will continue to fight it out. A problem a lot of people do is unintentionally make it worse by either picking what dog they want as the leader,generally by picking the first dog. So it is the best way to stop fights is by letting them sort it out,and with a muzzle they can do this without hard. Obedience refreshers are a good idea as well though so you can go through with that,and it will put YOU on top of the pack above her(as it should always be you and not any dog)